The present invention relates to available-time display and user-data backup in a battery-driven cellular mobile phone.
Japanese Laid-Open Publication No. 11-55372 discloses a technique in which in a portable phone, data on available time (available talk time and standby time) in terms of the terminal voltage of the battery is stored beforehand in a ROM, and the portable phone's available time corresponding to the remaining capacity of the battery is obtained for display from the measured value of the battery's terminal voltage. This technique improves the usability of the phone as compared with a case in which the remaining capacity of a battery in terms of its fully charged state is displayed in several levels in accordance with the terminal voltage of the battery.
In cellular phones, user data such as communication parameters, voice notes, a phone book and mail data is generated. Such user data is temporarily recorded in DRAMs, SRAMs or other volatile memory and then is backed up into a flash memory or other non-volatile memory.
Japanese Laid-Open Publication No. 2000-78070 discloses a technique in which backup of user data generated in a mobile phone is transferred to and stored in a memory backup center (for example, a radio base station) on a mobile communication network. According to this technique, as long as backup of the user data is made on a regular basis, even if the mobile phone has been lost, necessary data can be obtained from the network by another cellular phone, which therefore improves the ease of use.
Nevertheless, since the conventional available-time display technique uses the data stored in advance in the ROM, if characteristics of the battery have changed due to deterioration of the battery or changes in the battery temperature, an accurate available time cannot be obtained.
Further, if the above-described user-data backup operation is frequently performed, the battery becomes exhausted needlessly. Suppose for example a case in which the backup destination is a flash memory. Since the flash memory permits writing only in block units, even if the data that needs to be rewritten is just a single byte, it could only be written into the memory in units of, e.g., several dozen bytes, meaning that power for writing several dozen bytes' worth of data would be used up. Therefore, if a backup is made and stored into the flash memory each time new user data is registered, the battery would be consumed significantly, which would result in a shorter available time.